The following additional abbreviations are defined as follows:
3GPP third generation partnership project
BW bandwidth
CAZAC constant amplitude zero autocorrelation
CDMA code division multiple access
CP cyclic prefix
CQI channel quality indication
DL downlink (Node-B to UE)
FDM frequency division multiplex
FDMA frequency division multiple access
IRC interference rejection combining
LTE long term evolution of UTRAN
MIMO multiple input/multiple output
Node B base station
PAR peak-to-average ratio
RAN radio access network
RNC radio network controller
SB1 short block #1 (the first pilot symbol)
SB2 short block #2 (the second pilot symbol)
SIMO single input/multiple output
TDM time division multiplex
TTI transmission time interval
UE user equipment, such as a mobile station or mobile terminal
UL uplink (UE to Node B)
UTRAN-LTE universal terrestrial radio access network-LTE (may be referred to as 3.9G)
Standardization discussions have taken place related to the UTRAN-LTE UL reference signal structure. Reference in this regard may be had to 3GPP RAN1 #44 bis Meeting, Athens, Greece, 27-31 Mar. 2006.
Three different options generally shown in FIG. 2 have been considered. There are assumed to be two pilot blocks, SB1 and SB2, in each UL sub-frame. Thus far, the assumption has been that the CDMA-based approach (CAZAC with cyclic shifts) is applied for both pilot blocks (SB1, SB2). A Distributed FDMA approach has also been considered.
One problem that arises concerns how to combine the in-band pilot transmission and out-band/out-time pilot transmission (e.g., channel sounding for UL CQI estimation) in such a way that both channel estimation and CQI estimation perform adequately. Additional concerns relate to reference signal design.
Issues that arise and should be addressed include the following: flexibility in terms of bandwidth allocation (this contributes to the gain potential of the channel dependent scheduling); PAR properties; channel tracking capability (how many simultaneous users can be maintained in the sounding mode); the required DL signaling; and implementation complexity.
A conventional approach is illustrated in FIG. 3A for an example of four sub-frames and 12 frequency sub-bands. Two approaches have been considered in this regard: both pilot blocks SB1, SB2 are transmitted using the entire scheduling BW (sub-bands 3-6, as shown in FIG. 3A); and one of the pilot blocks is transmitted using the signal bandwidth, while the other pilot block is transmitted using the scheduling bandwidth (or with the system bandwidth).
In both approaches the pilot code(s) are user-specific.
General reference may be had to 3GPP TR 25.814 V1.2.2, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Layer Aspects for Evolved UTRA (Release 7),” Apr. 4, 2006.